Radiation attenuating comb assembly

ABSTRACT

There is disclosed a beam-attenuation comb assembly for doublebeam, optical null spectrophotometers comprising a major and minor comb adapted for mutual registration. The major comb has a single wedge shaped aperture and the minor comb a pair of similarly shaped apertures. In operation the assembly is driven in the manner well known in the art. Upon actuation of a solenoid, the major and minor comb assembly is disengaged and only the minor comb is driven to achieve beam balancing. Since the change in attenuation per unit displacement of the minor comb is different than that for the major and minor comb assembly, a scale expansion is achieved.

United States Patent 1151 3,685,885 Scott [451 Aug. 22, 1972 RADIATION ATTENUATING COMB 2,896,508 7/1959 Biedermann ..250/237 X ASSEIWBLY Primary Examiner-Rona.ld L. Wibert [72] Inventor. gfiillznrtlgaliltgony Scott, Glenrothes, Assistant Examiner F L Evans Attorney-Paul R. Harder and Robert J. Steinmeyer [73] Assignee: Beckman Instruments, Ltd., Glenrothes, Fife, Scotland [57] ABSTRACT [22] Filed: Oct. 2, 1970 There is disclosed a beam-attenuation comb assembly for double beam, optical null spectrophotometers App! 77'666 comprising a major and minor comb adapted for mutual registration. The major comb has a single wedge [30] Foreign Application Priority Dat shaped aperture and the minor comb a pair of similarly shaped apertures. ln operation the assembly Oct. 17, 1969 Great Bntam ..50,995/69 is driven in the manner we" known in the an Upon actuation of a solenoid, the major and minor comb as- U-S. embiy is disengaged and only the minor comb is 1 driven to achieve bean} balancing Since the change in Fldd Search attenuation per unit displacement of the minor comb 356/89 is different than that for the major and minor comb assembly, a scale expansion is achieved. [56] References Cited 2 Claim, 7 Drawing Figures UNITED STATES PATENTS 1,849,607 3/l932 Bernheim ..350/272 X Y s-wsk PATENTEU M1922 3 685 885 sum 2 0f 3 RADIATION ATTENUATING COMB ASSEMBLY This invention relates to apparatus for use in a spectrophotometer, and more particularly to a beam-attenuation comb-assembly.

In a known spectrophotometer of the double beam type a servo motor is provided to position a unitary comb-assembly selectively in the path of the reference beam to attenuate the energy thereof and thereby achieve an energy balance between the two beams of the spectrophotometer. The servo motor is responsive to any difference in the energies of the two beams to drive the comb-assembly so as to reduce a said difference to substantially zero, and the attenuation of the reference-beam energy is proportional to the movement or translation of the comb assembly from a datum position. Read-out means for indicating the attenuation is driven by the servo motor. In order to provide scale expansion of the read--out means of this known spectrophotometer the said difference signal is electronically amplified by a specified scale factor and is fed in amplified form to the servo motor in order more exactly to achieve an energy balance between the two beams. The read-out means operates with a corresponding scale factor. This system however has the disadvantage that there is no improvement in the photometric resolution of the remainder of the spectrophotometer since the noise component of the said difference signal is amplified to the same extent as the actual energy-difference indicating component of the difference signal.

It is an object of the present invention to provide an improved form of comb-assembly so as to obviate or mitigate the above disadvantage when the improved comb-assembly is used in a spectrophotometer.

According to the present invention there is provided apparatus for use in a spectrophotometer, comprising first and second apertured members adapted for mutual registration to provide a beam-attenuation combassembly having a predetermined attenuation characteristic, said members being selectively adjustable in mutual disposition away from said mutual registration to vary said characteristic selectively within predetermined limits.

Further according to the present invention there is provided a method of attenuating the energy in an energy beam of a spectrophotometer, said method comprising the steps of intercepting the energy beam with a two-part comb-assembly, the position of the composite assembly in the energy beam determining the attenuation thereof, and providing scale expansion for the read-out means monitoring the energy attenuation by disengaging the two parts of the comb-assembly and selectively translating one part thereof relative to the other part thereof.

An embodiment of the present invention will now be described by way of example with reference to the accompanying drawings, in which:

FIGS. 1A and B show major and minor combs together forming apparatus according to the present invention;

FIG. 2 shows the major and minor combs in assembled condition for use as a comb-assembly in the normal mode;

FIG. 3 shows the comb-assembly of FIG. 2 in the scale expansion mode;

FIG. 4 is a perspective view of the comb-assembly and associated components;

FIG. 5 diagrammatically illustrates a detail of the apparatus shown in FIG. 4', and

FIG. 6 is a block diagram of a control system for the comb-assembly when used in a spectrophotometer.

As shown in the drawings the apparatus according to the present invention includes first and second apertured members 10, 11 respectively in the form of minor and major radiation-beam attenuating combs. The major comb l l, which is rectangular in shape and made of thin gauge phosphor bronze or brass, contains a single wedge-shaped aperture 12 having parallel ends 13 and 14. The minor comb 10, which is also rectangular in shape and made of the same material as the comb 11, contains a pair of identical wedge-shaped apertures 15 and 15A which are symmetrically disposed about a longitudinal axis 17. The apertures 15 and 15A respectively have parallel ends l6, l8 and 16A, 18A, the ends 16 and 16A being spaced apart by the length of the end 13 of the aperture 12 in the major comb l l, and the length of the end 14 of the aperture 12 in the major comb 11 being equal to that of the two ends 18, 18A and the distance between the ends 18 and 18A of the minor comb 10. In this way the apertures of the two members 10, 11 have corresponding dimensions.

The combs 10, 11 are shown in an assembled or mutually registered condition in FIG. 2, for use in the normal energy-attenuation mode in the reference beam of a two-beam spectrophotometer, the aperture through which the radiation beam is to pass being indicated in broken lines at 20.

In operation the composite assembly is bodily translated laterally with respect to the aperture 20 as indicated by the arrow A, by means to be described hereinafter, and in this mode functions in a similar manner to a conventional comb-assembly.

FIG. 3 shows the composite assembly in the scale expansion mode wherein, in operation the major comb I] is held stationary and the minor comb 10 is translated laterally with respect both to the aperture 20 and to the comb 11.

A perspective view of the two combs and associated components is shown in FIG. 4 wherein the two combs l0 and 11 are mounted in a horizontal slideway 21 which is secured to an upright support 22. A servo motor 23 is provided which drives the assembly through a rack-and-pinion 24 connected to the comb 11, and which also actuates read-out means such as a pen recorder in response to the position of the assembly with respect to a datum position. The support 22 also carries a hinged horizontally-disposed runner 25 which is actuated by a solenoid 26 in order to disengage the minor comb 10 from the major comb ll. Clamping means may be provided if so desired to secure the comb 10 whilst it is disengaged from the comb 11.

A detail of the apparatus is shown in FIG. 5 to illustrate the mounting to the major comb 11 on the minor comb l0, and it will be seen that the minor comb carries an upstanding pin 27 which engages in a recess 28 in the major comb 11. The minor comb 10 also has an arm 29 projecting downwardly into the runner 25 so that when solenoid 26 is actuated the runner 25 is caused to move towards the support 22 thereby disengaging the pin 27 from the recess 28 and allowing the minor comb 10 to be driven independently of the major comb 1 l.

A control system for the apparatus when used in a spectrophotometer is shown in FIG. 6 and includes a source of radiation 30 which directs radiation along two paths 33, 34, one of which 33 contains the major and minor comb assembly, and the other of which 34 contains a sample 31 which is under test. The path 34 also contains an auxiliary comb 35 to limit the maximum energy transmitted to the sample 31, and a comparing device 36 is provided to compare the intensities of the beams emitted from the sample 31 and the comb-assembly. The output of the device 36 is amplified by an amplifier 37 which controls the servo motor 23 which in turn drives the minor comb 10 as above described.

The control of the solenoid 26 shown in FIG. 4 is by means of a manually-operated on/ofi switch 40.

In operation when the attenuation of the reference beam is found to be at or near a point of interest (i.e. at balance conditions) the operator actuates the on/off switch 40 to select scale expansion which automatically disengages the major and minor combs 10, 11 causing the servo motor 26 to drive the minor comb l alone. The degree of attenuation available from the maximum movement of the minor comb l0 alone is a predetermined proportion of the attenuation available from the maximum traverse of the composite assembly. The ef fective change in aperture available from the full travel of the assembly is therefore reduced by this scale factor. In the illustrated assembly this scale factor is :1.

Thus the total change in attenuation is only one-fifth or percent of the nominal value set by the assembly when in the normal mode and this is in two portions, nominal +X percent and nominal Y percent depending upon the direction of movement away from the nominal; X Y percent being equal to 20 percent. For example if the nominal attenuation is 60 percent of the maximum the available scale expansion will be in the range 60 percent 1/5 of 40 percent 60 percent 1/5 of 60 percent Le. 48 percent to 68 percent of the maximum available.

The pen of the recorder, although moving through the same distance in scale expansion mode as in the normal mode does so at a different scale as indicated above and this scale may be calculated and adjusted automatically by means (not shown) and a numerical read-out provided if so desired.

In a modification the major comb is mounted for movement towards and away from the minor comb and the solenoid 26 is actuable selectively to engage or release the major comb from the assembly. Also, the two comb members may have a plurality of apertures arranged in groups with corresponding dimensions as described hereinbefore.

What we claim is:

1. Apparatus for use in a spectrophotometer comprising:

first and second aperture members adapted for mutual registration and mutual translational movement in each direction from a datum position to provide a beam-attenuation comb assembly for increasing and decreasing the intensity of a beam transmitted thereby; releasable locking means securing said first and second aperture members one to the other for mutual translational movement;

drive means connected to one of said members for translating said members in either direction thereby to provide a first predetermined attenuation characteristic when said members are secured together for mutual translational movement; and means for actuating said releasable locking means to disengage said first and second members one from the other whereby only the driven member is translated by said drive means to provide a second predetermined attenuation characteristic.

2. The apparatus according to claim 1 wherein one of said members has a pair of similar wedge-shaped apertures therein and the other has a wedge-shaped aperture of corresponding dimensions to the apertures of said one member. 

1. Apparatus for use in a spectrophotometer comprising: first and second aperture members adapted for mutual registration and mutual translational movement in each direction from a datum position to provide a beam-attenuation comb assembly for increasing and decreasing the intensity of a beam transmitted thereby; releasable locking means securing said first and second aperture members one to the other for mutual translational movement; drive means connected to one of said members for translating said members in either direction thereby to provide a first predetermined attenuation characteristic when said members are secured together for mutual translational movement; and means for actuating said releasable locking means to disengage said first and second members one from the other whereby only the driven member is translated by said drive means to provide a second predetermined attenuation characteristic.
 2. The apparatus according to claim 1 wherein one of said members has a pair of similar wedge-shaped apertures therein and the other has a wedge-shaped aperture of corresponding dimensions to the apertures of said one member. 